In a review manuscript by Samyn (Journal of Materials Science, 48: 6455-6498 (2013)), the means for imparting water resistance to cellulosics such as paper is detailed. Compounds such as abietic acid (from rosin), alkene ketene dimer, and alkenyl succinic anhydride are used. These reagents may impart high water resistance to paper with water contact angles up to 150°. In addition, in work disclosed by Sundholm and Alexander (U.S. Patent Application Publication 2012/0138249), the use of alkene ketene dimer and alkenyl succinic anhydride is also shown to provide increased hydrophobicity. Abietic acid may be a contact allergen, and requires the addition of aluminum salts to provide an insoluble material that will bind to the cellulose. This insolubility may lead to inhomogeneities in the final article. Alkene ketene dimer requires the use of some type of ketene in its synthesis; however, ketenes are hazardous chemicals which may require the use of hazardous acid chlorides in their synthesis. In addition, some amount of the ketene will react with water which will lead to non-effective ketones which will end up in the waste stream. Alkenyl succinic anhydrides, such as octenyl succinic anhydride, may cause severe skin/eye damage and may be an allergen. These anhydride reagents may also react with water and not bind to the cellulose. Both the ketene and anhydride methods require tight pH control during their application steps. These ketene and anhydride routes use either costly ingredients, are themselves hazardous chemicals, or they are synthesized from hazardous chemicals.
Yoon and Deng (Tappi Journal, 5: 3-9 (2006)) showed that starch-fatty acid complexes imparted increased hydrophobicity to paper. However, these complexes had limited solubility (must be kept above 70° C.) which made it necessary to incorporate clay into the paper formulation. The low solubility may cause complications in an industrial process.
Dellinger et al. (U.S. Patent Application Publication 2014/0186644) disclosed the production of water resistant paper through the use of an amide wax combined with a cellulose ester, shellac, and rosin. In addition, phospholipids or medium-chain length triglycerides were used to give increased performance. These compounds require the use of flammable solvents (such as propyl acetate or acetone) for them to be coated onto paper. When these solvents evaporate they may be considered as volatile organic compounds and must be controlled.
Hormi et al. (Journal of the American Oil Chemists Society, 79: 921-930 (2002)) detailed the use of long-chain fatty amine quaternary salt derivatives in modifying the surface properties of paper. These ammonium salts were produced from the corresponding fatty acids after reaction with glycidyl trimethylammonium chloride or by the reaction of a long chain amines with epichlorohydrin or epibromohydrin. These reagents are hazardous materials that require sophisticated equipment to handle them safely.
Geissler et al. (Cellulose, 21: 357-366 (2014)) utilized cellulose stearoyl ester nanoparticles to impart improved water resistance to paper. Water contact angles of up to 154° were obtained. The nanoparticles were produced using stearoyl acid chloride (˜15:1 versus cellulose), pyridine (˜25:1 versus cellulose), methylene chloride, acetone, and cellulose. The numerous hazardous reagents and the large amount of hazardous waste negate the benefits resulting from biodegradability.
As detailed in a review manuscript by Thuo et al. (Coatings, 5: 1002-1018 (2015)), silanes are a common class of compounds which can be used to treat cellulosic surfaces, such as paper or cotton, in order to improve their water resistance. The silane compounds of interest utilize a silyl-chloride bond as the active site for bonding to the cellulosic surface. Chlorosilanes are very hazardous chemicals that require significant investment to handle safely. Often the silane compounds will have fluorinated groups bound to them to impart additional hydrophobicity to the coating. These fluorinated groups are produced either through the use of fluorine gas or hydrofluoric acid, both of which are very hazardous.
Hess et al. (Surface & Coatings Technology, 195: 121-129 (2005)) and Song et al. (Hydrate Polymers, 92: 928-933 (2013)) produced modified cellulosic articles that have improved hydrophobic properties through the plasma induced deposition of fluorocarbons or acrylate monomers respectively onto cellulose. Using this technique, water contact angles of 100-110° were obtained. However, the production of fluorinated compounds requires the use of many hazardous chemicals and processes. In addition, treatments that require the production of a plasma will entail additional costs.
Hu et al. (Colloids and Surfaces A: Physiochem Eng. Aspects, 351: 65-70 (2009)) produced a cellulosic article with water contact angle exceeding 130°. The technology developed by them requires a 3 component system using precipitated calcium carbonate, stearic acid, and a polymer latex. The latex is composed of a copolymer of styrene and acrylate. The technology does not utilize renewably sourced materials nor is it completely biodegradable. Similarly in a review article by Gaikwad and Ko (Journal of Materials Sciences and Engineering, 4: 1-5 (2015)) the use of clays in providing improved water resistance to paper is described. However, again the necessity for a non-biobased/non-biodegrable latex to bind the clay to the paper is a drawback of these technologies.
Yan et al. (Progress in Paper Coatings, 76: 11-16 (2013)) developed cross-linked cationic latexes that contained epoxy and quaternary ammonium groups that imparted improved water resistance to paper. The commercial purchased latex was combined with a polymer composed of styrene, butyl acrylate, dimethylaminoethyl methacrylate, stearyl methacrylate, and epichlorohydrin. This complicated mixture of materials did not utilize renewably sourced material nor is it completely biodegradable.
Wang et al. (“Preparation and property of waterborne UV-curable chain-extended polyurethane surface sizing agent: Strengthening and waterproofing mechanism for cellulose fiber paper”, Journal of Applied Polymer Science, DOI 10.1002/APP.43254) and Zhu et al. (“Properties and paper sizing application of waterborne polyurethanemicroemulsions: Effects of extender, cross-linker, and polyol”, Journal of Applied Polymer Science, DOI 10.1002/APP.43211) each developed polyurethane systems that imparted increased water resistance to paper. Each system provided benefits; however, they utilize hazardous isocyanate reagents as well as other hazardous reagents which would entail higher cost. The resulting agents would not utilize renewably sourced materials nor is it completely biodegradable.
Knaup and Gasafi-Martin (WO 2016000831 A1) disclosed the use of fluorinated polyacrylate compositions for use in imparting textiles, preferably cotton or cotton blends, with increased water resistance. The composition was made up of at least three different (meth)acrylic acid esters, one of which is fluorine-containing, and a paraffin wax, and other ingredients such as blocked isocyanates, polysiloxanes, or melamine resins. This complicated mixture would entail high cost, requires the use of hazardous non-biobased chemicals, and would not be biodegradable.
Iselau et al. (Colloids and Surfaces A: Physiochem Eng. Aspects, 483: 264-270 (2015)) utilized nanometer sized organic particles which after deposition on paper provided increased water resistance, as evidenced by having higher contact angles (50-98°) than the control. These particles were produced using a mixture of styrene, t-butyl acrylate, and n-butyl acrylate coupled with a cationic surfactant mixture composed of styrene, dimethylaminopropyl methacrylamide, and 2-dimethylaminoethyl methacrylate. These reagents are hazardous, require complex organic synthesis, and are not biobased nor biodegradable.
Thus there exists a need for environmentally friendly means using biodegradable renewably sourced materials for imparting water resistance to cellulosics such as paper.
Steam jet cooking, as described in Fanta et al., Carbohydrate Polymers, 98: 555-561 (2013), is a rapid and continuous process that is used to prepare aqueous dispersions of starch for commercial applications (Klem, R. E., and D. A. Brogley, Pulp & Paper, 55: 98-103 (1981)). In our labs, our small scale jet cooking equipment uses the excess steam jet cooking technique (Fanta et al., Carbohydrate Polymers, 98: 555-561 (2013)) to produce the complexes. However, the other technique, thermal-jet cooking, can perform a similar function and provide the starch complex. The choice of which type of steam jet cooking to use will generally be dependent on the equipment that each company has. This process has been used commercially for decades to prepare starch solutions for non-food applications such as paper in order to impart wet/dry strength and to alter the surface properties of the paper, such as the absorption of ink. This process involves pumping an aqueous starch slurry through a heating device consisting of specially configured orifice leading to a chamber where the slurry is instantly mixed with steam at high temperature and pressure. The intense turbulence that results from the condensation of high pressure steam and the passage of excess steam through the cooker not only promotes rupture and dissolution of starch granules but also leads to mechanical shearing of starch macromolecules. If the starch being used is high in amylose content (greater than 50%, such as AmyloGel™ 03003, Cargill Inc.), then the structure of the starch will revert back to its original form, a process called retrogradation, and the starch will no longer be soluble. It has been shown that by adding a fatty acid salt or fatty ammonium salt to steam jet cooked amylose starch solution, while still hot, that a water soluble inclusion complex will form (Byars et al., Carbohydrate Polymers, 88: 91-95 (2012); Fanta et al., Carbohydrate Polymers, 98: 555 (2013)). With adjustments in pH, the rheology of the complexes formed from amylose corn starch and the sodium salts of fatty acids will change dramatically (Byars et al., Carbohydrate Polymers, 88: 91-95 (2012)). None of these reports, nor any other publications to date, mention anything about how the high amylose corn starch and fatty ammonium salts (or its amine) interact with cellulosic articles, such as paper or cotton fabrics. We found that when these high amylose corn starch and fatty ammonium salt complexes are applied to cellulosic articles, surprisingly the surface of the article had increased hydrophobicity (as measured using water contact angle, where the water contact angle increases versus a control). After an application of dilute base to convert the ammonium salt of the complex to its free base form, the degree of hydrophobicity surprisingly increases (as measured by increasing contact angle). The described complexes are inherently much safer than other technologies that provide similar properties. In addition, these complexes are produced from renewable materials and are completely biodegradable.